System for transmitting communications



W. M. HAHNEMANN ET AL SYSTEM FOR TRANSMITTING COMMUNICATIONS .Filed July 10, 1957 2 Sheets-Sheet 1 Jifozvzey 1939- w. M. HAHNEMANN ET AL v 8 ,835

SYSTEM FOR TRANSMITTING COMMUNICATIONS l Q va V 2 A g o Patented Dec. 26, 1939 PATENT oFFicE SYSTEM FOR TRANSMITTING C'OIVHVIUNIOATIQNS Walter Max Hahnemann,

Berlin-Marienfelde,

and Alfred Wiessner, Berlin-Tempelhof, Germany, assignors to C. Lorenz Aktiengesellschaft, Berlin-Tempelhof, Germany, a com- Application July 10, 1937, Serial No.'153,074

In Germany March 13, 1934 13 Claims.

This invention relates to new and useful improvements in highand low-frequency transmission of intelligence, particularly over cables.

The invention has for its object so to construct the subscribers stations that the subscribers may use them without any circuit change whether it is desired to employ highor low-frequency. Subscribers stations as provided by the invention present the advantage that the high frequency generators may be disposed in the exchange stations without requiring feed-back suppressors.

If in accordance with prior arrangements low frequency talking-connections were arranged between the subscribers stations and the exchange, the intercommunication of the exchanges thus being by means of high frequency carrier waves, then it would be necessary to employ feed-back suppressors disposed where in the exchanges the change from the two-wire path to the four-wire path occurs. A four-wire path may be spoken of here inasmuch as the high frequency connection is in both directions effected with the aid of separate carrier waves. The expressions twowire and four-wire are here retained although high frequency connections are concerned, the fundamental considerations being valid irrespective of kind of the transmitting medium.

The novel construction of the subscribers stations allows of leaving the high frequency generators in the exchanges as has been the case heretofore, in order that skilled attendants shall be available.

The invention will be understood from the following description, reference being had to the accompanying drawings in which Fig. l is a wiring diagram illustrating the fundamental idea of the invention, that is, the arrangement of the talking paths. Figs. 2 to 4 each show a wiring diagram of the subscribers station. Fig. 5 is a wiring diagram representing a special construction of the exchanges. Fig. 6 is a View similar to Fig. 5 and shows a slight modification of the arrangement illustrated there.

The relay contacts are shown at rest.

In Fig. 1, A and B denote the subscribers stations while VI and V2 indicate the exchanges. The arrows n designate low frequency whilst the arrows h denote modulated high frequency. The trafiic outgoing from A passes in low frequency fashion to the exchange VI. Here the low frequency acts to modulate the carrier high frequency wave. The modulated high frequency however does not only pass to the exchange V2 but flows to the subscribers station B. The reverse applies for the traific outgoing from B, that is to say, the transmission from B td V2 is by low frequency whilst the transmission from V2 to subscriber's station A is by high frequency. The high frequency carrier waves are different from each other. No feed-back suppressors are here 5 necessary.

Microphone and. telephone, usually comprised in one hand set, are for clearness shown separately in Figs. 2 to 4. The two talking wires are designated a, b.

In the arrangement represented in Fig. 2 th microphone M is located between the wires a, h, high frequency chokes H being connected in advance thereof which however are not absolutely necessary to provide. The telephone T is on the 15 one hand connected directly to the wires a, b, only high frequency chokes likewise designated H being if desired-interposed between T and the wires on, b, and is-on the other hand connected to the output terminals of a rectifier G. This recti- 20 fier, which may be a dry rectifier, is joined to the wires a, I; over condensers C. Whenever low frequency is supplied to this subscribers station, disclosed in Fig. 2, over a, b the rectifier will be ineffective on account of the condensers 0 con- 25 nected in advance thereof. If however high frequency is supplied to this station then telephone T cannot of course respond under the direct influence thereof. This high frequency is rectified by the device G so that the telephone shall re- 30 ceive low frequency. It is thus of no influence upon the subscribers station whether the conversation arriving over the wires (1, b is transmitted in low frequency fashion or by high frequency.

In order to prevent the subscriber from hear- 35 ing his words in the telephone the arrangement shown in Fig. 3 may be adopted. Here a split circuit I in which a microphone M is included and which is connected to the wires a, b over high frequency blocking means H, acts to energize 40 winding I of the telephone T. In the case of low frequency operation therefore the intercommunication is effected in the usual manner. On changing from low frequency traflic to high frequency trafiic arriving over a, b the high fre- 5 quency will be prevented by the blocking means H from entering the split circuit I and will pass over low frequency arresters Nand rectifier G to the Winding 2 of the telephone T. The windings I, 2 are so designed. that no transmission shall 5 occur between them. By thismeans the voice current is completely converted into sound en'- ergy, being prevented in this way from returning to line a, b over thewindings 2, l and circuit I.

In the arrangement shown in Fig. 4 a split cir- 55 cuit with microphone M and telephone T is in the case of low frequency traffic likewise connected to the wires a, b. 0n changing to high frequency trafiic a relay AA is in well known manner energized over a condenser Q by continuous currents arriving from the exchange. Relay AA closes its contact a3 and thus remains energized as long as continuous voltage is acting on it. Relay AA also has a break contact al and an alternate contact a2. Therefore on the response of relay AA contact a! is opened while contact a2 is switched over. By opening contact al the advantage is attained that the microphone shall be joined to the talking wires a, b with the avoidance of that attenuation which would be caused by the split circuit, whilst the switched contact a2 acts to connect telephone T to the wires a, I) over a high frequency rectifier G and low frequency arresters N.

This arrangement thus allows of changing from high frequency service to low frequency service without the subscriber having to do anything in this regard, and also acts to avoid an unwelcome attenuation of the microphone currents.

Figs. 5 and 6 each show an example of an arrangement by which preferably in the case of long distance service the communications shall arrive in the subscribers station in high frequency fashion even if in the exchange they arrive in low frequency fashion, for example along repeatered two-wire or four-wire circuits. This does away with the necessity for a split circuit on the exchange side and subscriber side and also avoids a balancing network having to be provided on the exchange side.

In the incoming direction of a four-wire long distance circuit F, Fig. 5, that serves for the low frequency transmission of communications a modulator M is located after an amplifier V. This modulator receives its carrier frequency from a generator disposed in the exchange, for instance, and common to several junction circuits. A side band with carrier passes over the 7 low frequency arresters N to the exchange jack K and thus over the local line to the subscribers station. The voice currents arriving from the subscribers station pass over the high frequency blocking means H into the outgoing toll line direction. In the case of selector service a repetition by relays is provided instead of the jack K. The carrier frequency is so chosen that in the local cable the difference of attenuation between high frequency and low frequency shall be as small as possible and that further the symmetry and avoidance of cross-talk shall be sufficiently great.

The connection of a long distance circuit having two line wires D is according to Fig. 6 made with the aid of a split connection P. In other respects the arrangement is here the same as that shown in Fig. 5.

What is claimed is:

1. A system for transmitting communications, comprising in combination with talking wires and subscribers stations having each a telephone and a microphone, a split circuit including the microphone, high frequency blocking means connecting said circuit to the talking wires, a winding in the telephone by which the latter is joined to said split circuit, a second winding in the telephone, a high frequency rectifier connected in circuit with said second winding, and a low frequency arrester connecting said rectifier 15 to the talking wires.

2. In a system according to claim 1 means for preventing the two telephone windings from influencing each other.

3. A system according to claim 1, having an exchange and means under control of said exchange for changing from low frequency service to high frequency service.

4. A system according to claim 1, having an exchange and a relay under control of said exchange, contacts controlled by said relay to open that part of the said split circuit in which the microphone is not included and at the same time to connect the telephone to the circuit of the high frequency rectifier.

5. A system according to claim 1, having an exchange and a relay adapted to be energized by continuous currents arriving from said exchange, and contacts controlled by said relay to open that part of the said split circuit in which the microphone is not included and at the same time to connect the telephone to the circuit of the high frequency rectifier.

6. A system for transmitting communication, comprising a first and a second telephone exchange, wires for low frequency transmission in both directions between said exchanges, a first subscribers station connected to said first exchange and including means for generating speech frequency currents for transmission to said first exchange and then over said wires to said second exchange, a second subscribers station connected to said second exchange and including means for generating speech frequency currents for transmission to said second exchange and then over said wires to said first exchange, means in said second exchange for generating high frequency currents, means in said second exchange for modulating said high frequency currents with the speech frequency currents arriving over said wires from said first exchange and. for transmitting said modulated high frequency currents to said second subscribers station, and means at said second subscribers station for demodulating said modulated high frequency currents and reproducing therefrom speech frequency sound waves.

'1. A system according to claim 6, wherein the means to modulate the high frequency currents is a modulator included in the wires that serve for the incoming low frequency transmission, and a low frequency arrester between said modulator and a subscribers station.

8. In a system of the character described, twowire telephone subscribers lines, each having a subscribers telephone station, a central telephone exchange with which said lines are associated, means for transmitting speech forming one side of a two way conversation from said exchange to a subscribers station at carrier frequency, and means for transmitting speech forming the other side of said same conversation to said exchange from the same station at speech frequency.

9. In the system defined in claim 8, a direct connection between a station and the associated nection between a station and the associated line, and another connection between said station and line including a high-frequency rectifier.

10. In the system defined in claim 8, a connection between a station and the associated line including a low-pass filter, and a second connection between said station and line including a high-pass filter and a rectifier.

11. A system as defined in claim 8, wherein said station includes a telephone receiver, further comprising a high frequency arrester for connecting said receiver with the associated line, and another connection between said receiver and said line including a rectifier.

12. In the system according to claim 8, a microphone at each station, and a high-frequency blocking means between each microphone and the associated line.

13. A system for transmitting communication, comprising a first telephone exchange, a second telephone exchange, connecting means for transmitting high frequencies in both'directions between said exchanges, a first subscribers station connected to said first exchange and having means for generating speech frequency currents and transmitting them to said first exchange, means at said first exchange for converting said speech frequency currents received from said first subscribers station into high frequency currents and transmitting them to said second exchange, means at said second exchange for transmitting such high frequency currents received from said first exchange directly to said second subscribersstation without demodulation, means at said second subscribers station for demodulating said received high frequency currents, means at said second subscribers station for generating and transmitting to said second exchange speech frequency currents, means at said second ex- I change for converting such speech frequency currents received from said second subscribers station into high frequency currents and transmitting them to said first exchange, means at WALTER MAX HAHNEMANN. ALFRED WIESSNER. 

